Significance of amplified fragment length polymorphism in identification and epidemiological examination of Candida species colonization in children undergoing allogeneic stem cell transplantation

Abstract

Candida albicans and non-C. albicans Candida species are increasingly being isolated from patients in high-risk categories, most notably, those who have undergone stem cell transplantation (SCT). Identification of the presence of non-C. albicans Candida species early in the course of the transplant procedure is important, as these species exhibit different sensitivities to the available antifungal treatments and cause mortality at rates that vary from those for C. albicans. Amplified fragment length polymorphism (AFLP) analysis has been shown to be a reliable method of reproducibly identifying medically important Candida species. We investigated the use of serial AFLP analysis of 54 routine surveillance cultures for the identification and epidemiological examination of Candida sp. colonization in five consecutive children undergoing allogeneic SCT. One child became colonized with a C. albicans strain and remained colonized with this strain during the whole admission period. Another child had persistent colonization with a C. albicans strain with striking variations in its AFLP patterns over time, which was considered indicative of microevolution. Candida dubliniensis, Candida lusitaniae, and Saccharomyces cerevisiae were identified in the three remaining patients, with two children being simultaneously and transiently colonized with different species. These findings show that colonization with yeasts during transplantation is a complex and dynamic interaction between the host and the organism(s). In our study three strains from eight separate time points were incorrectly identified as C. albicans by a rapid enzyme test. AFLP analysis of surveillance cultures allowed more accurate and informative epidemiological evaluations of pathogenic yeasts in children during transplantation.

FIG. 1.

Dendrogram obtained by AFLP analysis. Patients are coded by color blocks, as follows: patient 449, green; patient 501, yellow; patient 502, blue; patient 503, pink; and patient 505, red. The AFLP dendrogram clearly shows the clustering of bands for each species and strain that can be identified as specific for individual patients (in boldface) and identified by matching to a reference strain (ref. sample). The isolates from no two patients had identical patterns, clearly illustrating that nosocomial spread was not evident in the study population. DNA variations were seen within individual patient isolates, although the sequences of these isolates were mostly 90 to 95% similar to that of the original isolate, which is indicative of homology. *, one of the minimal additional bands associated with a fluconazole-resistant C. albicans isolate (patient 501); **, DNA variation, with the sequence of the isolate being <90% similar to that of the original C. albicans isolate from this patient (patient 505), suggestive of microevolution unrelated to the administration of antimicrobials.

FIG. 2.

Diagrammatic representation of the isolates obtained from various sites over time in relation to the occurrence of specific transplant events. The source of each isolate is (from top to bottom for each patient) throat, fecal, and perineal swab specimen cultures (specimens were obtained two times weekly). The color codes for the patients are as described in the legend to Fig. 1. *, patients who received treatment with oral fluconazole. The yeasts are represented as follows: C. albicans, ▩ and ; S. cerevisiae, ▧; C. lusitaniae, ; C. dubliniensis, ▨. UPN, patient number.